Laser inspection tool system

A method for measuring the height of a target object above a measurement surface, the method comprising the steps of:

• impinging the target object and the measurement surface with a first line of light at a first selected angle;
• impinging the target object and the measurement surface with a second line of light at a second selected angle, the second line of light being at a third selected angle to the first line of light;
• receiving an image of a first portion of the first line of light reflected by the target object;
• receiving an image of a first portion of the second line of light reflected by the target object;
• receiving an image of a second portion of the first line of light reflected by the measurement surface, the received image of the second portion of the first line of light being offset, as a function of the first, second, and third selected angles, from the received image of the first portion of the first line of light;
• receiving an image of a second portion of the second line of light reflected by the measurement surface, the received image of the second portion of the second line of light being offset, as a function of the first, second and third selected angles, from the received image of the first portion of the second line of light;
• determining the offsets of the received light reflected by the target object and the received light reflected by the measurement surface;
• calculating an uncorrected height of the target object above the measurement surface using the determined offsets and the first, second and third selected angles;
• calculating an alignment error using the determined offsets and the first, second and third selected angles;
• and
• calculating the height of the target object above the measurement surface using the uncorrected height and the alignment error.

An inspection tool for measuring the height of a target object above a measurement surface the inspection tool comprising:

• a remote tool head comprising:
• first and second light sources generating respective first and second lines of light, the lines of light projected at respective first and second angles onto the target object and the measurement surface, the first line of light being at a third angle to the second line of light;
• and
• a camera positioned to receive reflections of the first and second lines of light from the target object and the measurement surface;
• and
• a computer system in communication with the remote tool head, the computer system comprising:
• means for calculating offsets between the received light reflected by the target object and the received light reflected by the measurement surface;
• means for calculating an uncorrected height of the target object above the measurement surface and an alignment error from the first, second and third angles and the offsets;
• and
• means for calculating the height of the target object above the measurement surface from the uncorrected height and the alignment error.